Use QThreadPool to invoke free disk space checking jobs

Prevent the creation of an excessive number of threads.
PR #18347.
Closes #18202.

src/webui/api/freediskspacechecker.h

@@ -30,13 +30,13 @@
 
 #include <QObject>
 
-class FreeDiskSpaceChecker : public QObject
+class FreeDiskSpaceChecker final : public QObject
 {
     Q_OBJECT
     Q_DISABLE_COPY_MOVE(FreeDiskSpaceChecker)
 
 public:
-    FreeDiskSpaceChecker() = default;
+    using QObject::QObject;
 
 public slots:
     void check();

src/webui/api/synccontroller.cpp

@@ -32,7 +32,7 @@
 
 #include <QJsonObject>
 #include <QMetaObject>
-#include <QThread>
+#include <QThreadPool>
 
 #include "base/bittorrent/cachestatus.h"
 #include "base/bittorrent/infohash.h"
@@ -49,7 +49,6 @@
 #include "base/utils/string.h"
 #include "apierror.h"
 #include "freediskspacechecker.h"
-#include "isessionmanager.h"
 #include "serialize/serialize_torrent.h"
 
 namespace
@@ -372,15 +371,7 @@ namespace
 
 SyncController::SyncController(IApplication *app, QObject *parent)
     : APIController(app, parent)
-    , m_freeDiskSpaceChecker {new FreeDiskSpaceChecker}
-    , m_freeDiskSpaceThread {new QThread}
 {
-    m_freeDiskSpaceChecker->moveToThread(m_freeDiskSpaceThread.get());
-
-    connect(m_freeDiskSpaceThread.get(), &QThread::finished, m_freeDiskSpaceChecker, &QObject::deleteLater);
-    connect(m_freeDiskSpaceChecker, &FreeDiskSpaceChecker::checked, this, &SyncController::freeDiskSpaceSizeUpdated);
-
-    m_freeDiskSpaceThread->start();
     invokeChecker();
     m_freeDiskSpaceElapsedTimer.start();
 }
@@ -595,20 +586,27 @@ void SyncController::torrentPeersAction()
 qint64 SyncController::getFreeDiskSpace()
 {
     if (m_freeDiskSpaceElapsedTimer.hasExpired(FREEDISKSPACE_CHECK_TIMEOUT))
-    {
         invokeChecker();
-        m_freeDiskSpaceElapsedTimer.restart();
-    }
 
     return m_freeDiskSpace;
 }
 
-void SyncController::freeDiskSpaceSizeUpdated(qint64 freeSpaceSize)
+void SyncController::invokeChecker()
 {
-    m_freeDiskSpace = freeSpaceSize;
-}
+    if (m_isFreeDiskSpaceCheckerRunning)
+        return;
 
-void SyncController::invokeChecker() const
-{
-    QMetaObject::invokeMethod(m_freeDiskSpaceChecker, &FreeDiskSpaceChecker::check, Qt::QueuedConnection);
+    auto *freeDiskSpaceChecker = new FreeDiskSpaceChecker;
+    connect(freeDiskSpaceChecker, &FreeDiskSpaceChecker::checked, this, [this](const qint64 freeSpaceSize)
+    {
+        m_freeDiskSpace = freeSpaceSize;
+        m_isFreeDiskSpaceCheckerRunning = false;
+        m_freeDiskSpaceElapsedTimer.restart();
+    });
+    connect(freeDiskSpaceChecker, &FreeDiskSpaceChecker::checked, freeDiskSpaceChecker, &QObject::deleteLater);
+    m_isFreeDiskSpaceCheckerRunning = true;
+    QThreadPool::globalInstance()->start([freeDiskSpaceChecker]
+    {
+        freeDiskSpaceChecker->check();
+    });
 }

src/webui/api/synccontroller.h

@@ -31,7 +31,6 @@
 #include <QElapsedTimer>
 #include <QVariantMap>
 
-#include "base/utils/thread.h"
 #include "apicontroller.h"
 
 class QThread;
@@ -51,16 +50,14 @@ public:
 private slots:
     void maindataAction();
     void torrentPeersAction();
-    void freeDiskSpaceSizeUpdated(qint64 freeSpaceSize);
 
 private:
     qint64 getFreeDiskSpace();
-    void invokeChecker() const;
+    void invokeChecker();
 
     qint64 m_freeDiskSpace = 0;
-    FreeDiskSpaceChecker *m_freeDiskSpaceChecker = nullptr;
-    Utils::Thread::UniquePtr m_freeDiskSpaceThread;
     QElapsedTimer m_freeDiskSpaceElapsedTimer;
+    bool m_isFreeDiskSpaceCheckerRunning = false;
 
     QVariantMap m_lastMaindataResponse;
     QVariantMap m_lastAcceptedMaindataResponse;